The present invention relates to a tubular hollow made of fiber-reinforced synthetic or plastic material, particularly for use as struts or any other frame component in aircraft, space vehicles, or the like. The invention, moreover, relates to a method of making such a hollow as well as to structure for carrying out such a method.
The aircraft and space industry uses to an increasing extent fiber compound parts in lieu of metal parts because, on one hand, these new materials have a strength and stiffness which are quite comparable to the corresponding properties of metal while, on the other hand, components of basically the same configuration have a significantly lower weight as compared to metal parts. It has to be observed, however, that mechanical properties of fiber-reinforced compound components are an isotropic in contradistinction to the fact that the properties of metal are usually isotropic. On the other hand, loads are usually not expected to be omnidirectional so that fiber-reinforced parts can be constructed in such a manner that the strength-defining properties and features match the expected loads and load directions in an optimum fashion. Therefore, anisotropy is not necessarily a disadvantage, which means that, in fact, one can use these parts under significant savings of weight. An example here is, for example, struts or rotor blades in helicopter experiencing mechanical loads strictly along particular axes.
A significant problem exists in the interfacing of such a fiber-reinforced component with an applied force. For this reason, it is customary to use the fiber-reinforced component with metallic endpieces, fittings, or the like, upon which the force will act and which will distribute that force properly into the fiber-reinforced component. These additional metallic elements are usually bonded or otherwise mechanically fastened with the fiber-reinforced part. For example, it has been suggested to use the struts in the aircraft industry which are comprised of a tubular center part made of a fiber-reinforced synthetic and terminal heads are provided at the two ends of this tubular part, the heads being made of aluminum. However, such compound structure, consisting, in fact, of different materials, constitutes only a compromise, which means that the potential high-grade strength properties of the fiber-reinforced component are not fully utilized, and the low weight feasible by the utilization of these materials is to some extent compromised by the addition of metallic endpieces.
Further to the state of the art, reference is made to German Pat. No. 11 91 556 concerning, in particular, expansion molding. Thermal expansion molding is also described in the journal "FLUGREVUE INFORMATION," No. 5, Aug. 18, 1980, pp. 3 and 4. However, these references do not refer to the inherent problem of connecting endpieces to a lightweight part of structural material.